Interleaved analog-to-digital converters, henceforth called “converters”, are comprised of two or more component converters that sample a common signal at a common rate, but are skewed in sampling time to increase the aggregate sample rate of the system. The outputs of the components are time-interleaved into a common output in an order consistent with their sample timing.
Examples of time-interleaved analog-to-digital converters are described in a co-pending U.S. patent application entitled “CABLE GATEWAY USING A CHARGE-DOMAIN PIPELINE ANALOG TO DIGITAL CONVERTER”, Ser. No. 61/113,661 filed Nov. 12, 2008, and a co-pending U.S. patent application entitled “ERROR ESTIMATION AND CORRECTION IN A TWO-CHANNEL TIME-INTERLEAVED ANALOG-TO-DIGITAL CONVERTER”, Ser. No. 12/419,599 filed Apr. 7, 2009, the entire contents of each of which are hereby incorporated herein by reference in their entirety.
Time-interleaving can be a means of achieving high sample rates with a relatively low tradeoff factor in other parameters of consequence, such as size, cost and/or power. However, to achieve performance from the interleaved system that approaches the performance of a single component, all components in the system must be well-matched in their sample timings, amplitude responses and phase responses. Mismatches in these parameters, and possibly others, of the of the component converters degrade the spurious response of the aggregate system.
Calibration is often employed to reduce the mismatches of the components—calibration addresses the cause. Alternatively post-converter data processing may be employed to correct the errors using signal processing of the interleaved data—post processing addresses the effect. Both methods require some form of error detection and the method described here is equally applicable to both. Henceforth, “calibration” will is be used to describe either mismatch reduction or error correction.
Amplitude response mismatch is sufficient to demonstrate the merits of the method for interleaving described here. This should not, however, imply a limitation of this method to addressing only the amplitude mismatch problem.
Amplitude response mismatch can be described as the mismatch in the amplitude responses of the component converters wherein the amplitude response of any component converter can be characterized by a polynomial. Higher-order polynomial terms are, in general, more computationally expensive to calibrate. Consequently, only those terms necessary to achieve the desired spurious performance from the system are typically addressed. For the purposes of demonstrating the foregoing interleaved sampling method, it is sufficient to consider the zero- and first-order coefficients in the amplitude response polynomials. These coefficients represent the offset and gain of the components.